Isolation of a 16π‐Electrons 1,4‐Diphosphinine‐1,4‐diide with a Planar C(4)P(2) Ring

Herein, we report the first 1,4‐diphosphinine‐1,4‐diide compound [(ADC(Ph))P](2) (5‐Ph) (ADC(Ph)=PhC{(NDipp)C}(2); Dipp=2,6‐iPr(2)C(6)H(3)) derived from an anionic dicarbene (ADC(Ph)) as a red crystalline solid. Compound 5‐Ph containing a 16π‐electron planar fused‐tricyclic ring system was obtained by the 4e reduction of [(ADC(Ph))PCl(2)](2) (4‐Ph) with Mg (or KC(8)) in a quantitative yield. Experimental and computational results imply that the central 8π‐electrons C(4)P(2) ring of 5‐Ph, which is fused between two 6π‐electrons C(3)N(2) aromatic rings, is antiaromatic. Thus, each of the phosphorus atoms of 5‐Ph has two electron‐lone‐pairs, one in a p‐type orbital is in conjugation with the C=C bonds of the C(4)P(2) ring, while the second resides in a σ‐symmetric orbital. This can be shown with the gold complex [(ADC(Ph))P(AuCl)(2)](2) (6‐Ph) obtained by reacting 5‐Ph with (Me(2)S)AuCl. A mixture of 5‐Ph and 4‐Ph undergoes comproportionation in the presence of MgCl(2) to form the intermediate oxidation state compound [(ADC(Ar))P](2)(MgCl(4)) (7‐Ph), which is an aromatic species.